The novel gear design disclosed herein fulfills two economically important objectives which have long been of primary concern to gear manufacturers, namely.
1. to provide gears which can be manufactured at high production rates with remarkably reduced costs, and PA1 2. to increase the load-carrying ability of gears without increasing their size.
While this new design is expected to be of particular importance to plastic and powder metal gearing, it is equally applicable to the field of heavy duty bevel gears, especially automotive differentials. Such heavy duty bevel gears have traditionally been made by processes of metal cutting that have forced their design into well established patterns. With the advent of new and improved metal-forming techniques, some of the design limitations imposed by practical cutting methods have been removed, and manufacturers of gears can take advantage of the removal of these limitations to achieve advances in product improvement and/or economy. As an example of a bevel gear design proposed to take advantage of new metal forming techniques, an attempt has been made recently to revive the very old concept of tooth shrouding. However, such shrouding is merely the addition of web-like reinforcing sections across the ends of the tooth slots, and the teeth of such shrouded gears employ conventional tooth designs.
As different from such recent prior art attempts, it is the intent of the invention herein to take full advantage of the freedom and speed of production offered by new gear-forming processes and new materials, e.g., powder metal and plastics, by departing remarkably from all present tooth designs. This novel tooth shape disclosed herein includes two concepts which have been known for many years but have been seldom, if ever, used in commercial gear design: "elliptical" shape, and inclining teeth .Iadd.depthwise .Iaddend.relative to the pitch .[.line.]. .Iadd.element.Iaddend.. Those skilled in the art will recognize this latter concept as one proposed primarily for the purpose of gaining some small improvement in smoothness of motion transmission from tooth to tooth and that, whenever proposed, it has incorporated root and face surfaces of conventional straight line generatrices. The other concept, of elliptically-shaped gear teeth, was proposed more than fifth years ago in U.S. Pat. No. 1,390,414 as a means for improving tooth strength. Neither of these ideas has ever found acceptance in the gear industry, and never has it been known or even remotely suggested to combine these two separate, distinct and highly unusual concepts. However, this is exactly what is done to obtain the radical new concepts in tooth design which are disclosed herein, and these new concepts not only include considerations of improved geometry for tooth strength but also seek to optimize the efficiency and economy of the new manufacturing processes by making possible the utilization of die arrangements which are simpler and less expensive to make and maintain than the die formats required to produce gears of conventional prior art designs.
While it is anticipated that the tooth design of the invention will find particularly wide acceptance in the special field of bevel gears, especially in automotive differentials as stated above, this invention is broadly applicable to other fields of gearing such as spur gears and helical gears. It should be noted that although both preferred forms of the novel gear design disclosed herein are quite unconventional in appearance, they will be identified with the conventional gear terms "bevel" and "cylindrical," since the imaginary pitch surfaces of these novel gear forms are conical and cylindrical, respectively.